Blended ROAS is lying to you

If you're reporting one blended ROAS number across all your campaigns, you're making decisions based on a fiction.

I manage campaigns across PMax, Demand Gen, and Search for multiple brands. Early on, I made the mistake of blending them together. "Overall ROAS: 3.8x" sounds great in a client update. It's also completely useless for deciding what to do next.

Here's why:

PMax has its own rules

Performance Max optimizes across Search, Shopping, Display, YouTube, and Discovery, all at once. The only metric that matters here is ROAS. If PMax is delivering 4x+ ROAS, you scale the budget. If it drops below your break-even threshold (which you need to calculate from actual margins, not guesses), you pull back. Simple.

But the moment you blend PMax ROAS with Search ROAS, you lose the signal. PMax might be crushing it at 5x while Search is limping at 1.2x. The blend says 3.1x and you think things are "fine." They're not. Search is burning money.

Demand Gen is not a ROAS channel

This is the one most people get wrong. Demand Gen exists to drive awareness and consideration, not direct conversions. Judging it by ROAS is like judging a billboard by how many people walked into your store within the hour.

The right KPIs for DGen: cost per add-to-cart, cost per site visit, view rate on video assets. If you're getting cheap ATCs from DGen, it's working, even if the last-click ROAS looks terrible.

Search has its own KPIs too

Search is intent-based. Someone typed your product name into Google. The KPIs here: CTR (are your ads relevant?), click-to-ATC rate (is the landing page working?), and conversion rate. ROAS matters but it's a downstream metric: if CTR is high and ATC rate is low, the problem is your landing page, not your bidding.

The rule

Never combine these into one number. Report them separately. Optimize them with channel-specific KPIs. If a client or boss asks for "the ROAS," give them MER (marketing efficiency ratio = total revenue / total spend) and explain that it's the overall health metric, not the optimization lever.

The optimization levers are channel-specific. Always.